Contemporary geochemical composition and flux of aeolian dust to the San Juan Mountains, Colorado, United States

Dust deposition in the Rocky Mountains may be an important biogeochemical flux from upwind ecosystems. Seasonal (winter/spring) dust mass fluxes to the San Juan Mountains during the period from 2004 to 2008 ranged from 5 to 10 g m(-2), with individual deposition events reaching as high as 2 g m(-2). Dust deposited in the San Juan Mountains was primarily composed of silt- and clay-sized particles, indicating a regional source area. The concentrations of most major and minor elements in this dust were similar to or less than average upper continental crustal concentrations, whereas trace element concentrations were often enriched. In particular, dust collected from the San Juan Mountain snowpack was characterized by enrichments of heavy metals including As, Cu, Cd, Mo, Pb, and Zn. The mineral composition of dust partially explained dust geochemistry; however, based on results of a sequential leaching procedure it appeared that trace element enrichments were associated with the organic-, and not the mineral-, fraction of dust. Our observations show that the dust-derived fluxes of several nutrients and trace metals are substantial and, because many elements are deposited in a mobile form, could be important controls of vegetation, soil, or surface water chemistry. The flux measurements reported here are useful benchmarks for the characterization of ecosystem biogeochemical cycling in the Rocky Mountains.